Thermostat



y 1931. AA. THOMAS 1,803,982

THERMOSTAT Filed March 26. 1927 Z INVENTOR Patented May 5, 1931 PATENT OFFICE ADOLPH A. THOMAS, OF NEW YORK, N. Y.

'rnnamos'ra'r Application filed March 26, 1927., Serial 110. 178,839.

My invention relates to thermostats, and its object is to provide a thermostat of simple rugged construction and capable of operating with a snap action for abruptly breaking an electric circuit or performing any other intended function.

Briefly stated, my new thermostat comprises a bowed spring member held under tension, :1 thermostatic element movable un- 1 der the action of heat to force the spring member abruptly into a position of reverse curvature, and a connection whereby the thermostatic element on cooling automatically snaps the spring member back to initial position.

My invention will be understood from a detailed description of the embodiment illustrated in the accompanying drawings, in which- I Fig. 1 shows an electric thermostat constructed in accordance with my invention, the parts being shown in normal circuit-closing position;

Fig. 2 is a view similar to Fig. 1, with the parts in circuit-opening position;

Fig. 3 is an end view of Fig. 1 looking from left to right;

Fig. 4 represents a transverse cross-section approximately online 4-4 of Fig. 1 and Fig. 5 shows a modified form of mounting for the spring contact member.

The parts are mounted on a suitable base 10, which may be of insulating material. On the end posts 11 of base 10 is mounted a bowed spring member 12, which may be in the form of a curved strip or a dished diaphragm of elastic sheet metal. If the member 12 is a diaphragm, the base 10 will have an annular rim for supporting the circumferential edge of the diaphragm, as will be understood without further illustration. To make the drawings as simple as possible, I have shownv the spring member 12 in the'form of an arched strip secured at its ends to posts 11 by bolts 13 and 14, one of which (as bolt 14) may also act as a binding post for a conductor 15. In Fig. 5 the spring member 12 is supported by simply inserting the ends in angular recesses 16 on blocks or posts 17. At or near its central portion the bowed spring the thermostatic element A begins to cool and member 12 carries a bracket 18, which may simply consist of a strip or wire bent into rectangular shape, as shown in Fig. 4, and secured to the upper face of member 12 in any practical way, as by soldering, brazing, riveting, or otherwise. The lower cross-arm of bracket 18 is covered with an insulating sleeve 19 of suitable material, preferably asbestos, which insulates not only electrically but also thermally. By forming the bracket 18 of duralumin, it can be made very light and strong.

A thermostatic element A is suitably mounted at one end on base 10, as by means of bolts 20 and 21. The bolt 21 may be in the form of a binding post for connecting a conductor 22. The thermostatic element A is preferably of bimetallic construction, consisting of a brass strip 23 and an iron strip 24 (or equivalent metals) secured together over their entire length. The normal shape of element A is such that the free end thereof is in firm contact with the central portion of spring member 12 to close the electric circuit, as illustrated in Fig. 1. When the element A reaches a. predetermined high temperature, its free end moves or tends to move upwardly (as viewed in Fig. 1) and presses against the tensioned spring member 12 until the latter snaps into a position of reverse curvature, thereby abruptly breaking the circuit. This position of the parts is illustrated in Fig. 2. I want to make it clear, however, that the position of parts A and 12 in Fig. 2 is not to be regarded as mathematically accurate, but is rather a diagrammatic arrangement to make the drawing as clear as possible. The abrupt separation of element A and spring member 12 opens the circuit without arcing. The practical advantage of this will be understood by those skilled in the art without the need of any detailed explanation. The crossarm 19 of bracket 18 is so positioned that it does not interfere with the movement of member 12 to circuit-breaking position. The contact member 12 remains in this position until .-again acted upon by element A.

After the electric circuit has been broken,

move back to its original position. As the I free end of the cooling element A moves back toward base 10, it engages the insulated arm 19 of bracket 18 and thus exerts a pull on the bowed spring member 12 until the latter reaches a condition of tension in which it suddenly snaps to initial position in contact with thermostatic element A. This abruptly closes the electric circuit, which remains closed until the element A reaches a predetermined high temperature, whereupon the circuit is again opened suddenly in the manner previously described. Attention is called to the fact that the electric circuit is not closed when the downwardly moving end of the cooling element A engages the insulated arm 19. This is important, as otherwise the element A would begin to heat up again. The cooling of element A continues until the member 12 snaps into contact with it. It is not necessary that the circuit shall be closed through spring 12 and thermostat bar A, for separate contacts may be arranged for closing the circuit without using the parts 12 and A as electric conductorst ment A instead of member 12.

It will be seen from the preceding description that I have provided a thermostat of unusually simple construction, which at the same time is rugged and compact. The views in the drawings are not drawn to correct scale as in a shop drawing, but I have purposely exaggerated the dimensions of the parts in order to make the drawings as clear as possible. The thermostat as actually constructed is considerably smaller than the illustrations in the drawings. The two movable parts that comprise my new thermostat may be housed in a very little space and are therefore easily installed in such small electric appliances as flat-irons, heating pads, toasters, and the like. Although I have described in detail a certain specific construction,,I want it understood that my invention is not limited to what is shown in the drawings, for it is manifest that the basic principle of my invention may be embodied in other forms than herein set forth by way of illustration. hen I speak of a bowed spring member in the claims, I mean any practical form of curved, arched or dished member of elastic material so tensioned as to change its shape abruptly when sufficient external pressure is applied, the

member remaining in either shape until snapped out of it by the thermostatic element. Also, when in some of the claims I speak of the thermostat bar engaging the spring membe-r,'I do not mean, of course, that the thermostatic metal of the bar shall come in direct contact with the metal of the spring memher, because it is manifestly possible to eii'ect mechanical engagement of these parts through interposed contact buttons or heads which are usual in thermostatic devices.

I claim as my invention:

1. A thermostat comprising a-flat U-shaped snapped by said bar at predetermined temperature into a position of reverse curvature, said spring and said bar being mechanically disconnected and mounted to move in the same plane, whereby a fiat structure is produced, and connecting means carried by one of said movable parts whereby said bar on cooling becomes automatically coupled to the central portion of said spring and snaps it back to initial position.

2. A thermostat comprising a bowed spring adapted to change its curvature abruptly by external force, a bimetallic thermostat bar arranged to engage said spring substantially at the center thereof so as to exert pressure against the spring in a direction substantially radial to the curvature of the spring, whereby the latter is snapped by said bar at predetermined temperature into a position of reverse curvature, said spring and said bar being mechanically disconnected means for so mounting said spring and bar that they move in the same plane, whereby a flat structure is produced, and a substantially U-shaped yoke mounted on one of said movable parts for automatically coupling said bar on cooling to the central portion of said spring, whereby the latter is snapped back to initial position, said coupling yoke permitting movement of the spring independently of the thermostat bar.

3. A thermostat comprising a flat support having a pair of spaced arms, a buckling spring mounted at its ends in'said arms, a thermostat bar mounted on said support in the plane thereof and within the space defined by said arms, whereby a flat compact structure is produced, said thermostat bar on heating being adapted to exert pressure against the central portion of said spring until the latter snaps into reverse curvature, said spring and said bar being mechanically disconnected, and connecting means carried by one of said parts whereby said bar on cooling becomes automatically coupled to the central portion of said spring and snaps it back to initial position.

4. A thermostat comprising a flat unitary support, a bowed spring member mounted on said support and adapted to change its shape abruptly by external force, a bimetallic thermostat member also mounted on said support and movable under the action of heat to press against said bowe'd spring memberuntil the latter snaps into a position of reverse curvature, said members being mechanically disconnected and so mounted on said support that they move in the same plane, whereby a fiat structure is produced, and an extension secured to one of said members and arranged to engage the other member when said thermostatic member cools, whereby the movement of said thermostatic member in cooling exerts pressure against said spring member until the latter snaps back to initial position, said extension permitting movement of the spring member independently of the thermostatic member.

5. A thermostat comprising a flat unitary support, a bowed spring member adapted to change its shape abruptly by external force,

- a bimetallic thermostat element in the form of a bar connected at one end to said support and normally in contact with said bowed spring member, said bimetallic element being movable under the action of heat to press against said member until the latter snaps into a position of reverse curvature out of contact with said element, said member and element being mechanically disconnected and so mounted on said support that they move in the same plane, whereby a flat structure is produced, and a connection between saidmember and said element whereby the latter upon cooling engages said connection to ex ert a pull on said member until it snaps to initial position, said connection permitting movement of the spring member independently of the thermostatic element.

6. A thermostat comprising a U-shaped support, a bowed spring member mounted at its ends on said support and adapted to change its shape abru tly by external force, a bracket fixed on sai spring member at or near the center thereof, and a U-shaped thermostat bar connected at one end to said support and movable in the same plane as sald bowed spring member, said thermostat bar being normally in contact with said bowed spring member and movable under the action of heat to press against said member until the latter snaps into a position of reverse curvature out of contact with said element, said thermostatic element being so arranged that upon cooling it engages said bracket and thereby exerts pressure on said member until the latter snaps back to initialposition, said bracket permitting movement of the spring member independently of the thermostatic element.

7. A thermostat comprising a substantially U-shaped flat support, a buckling spring mounted at its ends between the arms of said support, a substantially U-shaped thermostat bar secured at one end to the base of said support and arranged'in the plane of said support, the free end of said bar being adapted to exert pressure against the central portion of said spring until the latter snaps into reverse curvature at predetermined high temperature, said spring and said bar being mechanically disconnected, and coupling means carried by one of said movable parts for automatically connecting the bar on cooling to the spring until the latter snaps back to initial position, said coupling means permitting movement of the spring independently of the thermostat bar.

ADOLPH A. THOMAS. 

